.back_control_btn {
  width: 50px;
  height: auto;
  position: absolute;
  top: 20px;
  left: 20px;
  cursor: pointer;
  display: none;
}

@media (max-width: 576px) {
  .back_control_btn {
    width: 35px;
    top: 15px;
    left:calc((100vw - var(--width-welcome)) / 2);
  }
}

@media (max-width: 320px) {
  .back_control_btn {
    width: 35px;
    top: 15px;
    left:calc((100vw - var(--width-welcome)) / 2);
  }
}